Method and apparatus for vertically calibrating wire of wire cutting electric discharge machine

ABSTRACT

A method and an apparatus for vertically calibrating a wire of a wire cutting electric discharge machine are provided. The vertical calibration apparatus includes a body, an upper calibration board and a lower calibration board attached to the body and parallel to the machine table, with a ring hole formed on the upper calibration board and on the lower calibration board respectively. The two ring holes have the same vertical axis. The method of wire cutting electric discharge machine vertical calibration comprises searching for the circle centers of the two ring holes by constantly touching the ring edge several times by the wire, then passing the wire through the circle centers. The method of determining the height of the upper holding guide and the lower holding guide for wire comprises utilizing formulae with given radii of the two ring holes, the height of the two ring holes relative to the table, the cone angle of the two ring holes with the same vertical axis, and a variable, which is a measurement from the upper holding guide or the lower holding guide located on the vertical wire passing the circle centers of the upper ring hole and the lower ring hole to a position of the inclined wire which touches the edge of the two ring holes.

FIELD OF THE INVENTION

[0001] The present invention relates to wire cutting electric discharge machines, and especially to a method and apparatus for vertically calibrating a wire of a wire cutting electric discharge machine and measuring the heights of the upper holding guide and lower holding guide.

BACKGROUND OF THE INVENTION

[0002] The prior art apparatus for vertically calibrating a wire of cutting electric discharge machine is illustrated in FIG. 1. An automatic vertical calibration device 1 has an upper calibration board 2 with a PX1 being coplanar with a surface PX2 of a lower calibration board 3, while surface PY1 of upper calibration board 2 is coplanar with a surface PY2 of the lower calibration board 3. The upper calibration board 2 and lower calibration board 3 are insulatively fixed to a main body 7. The surface PX1 and PX2 are respectively perpendicular to the surface PY1 and PY2, and these surfaces are all perpendicular to the bottom of the main body 7 and a horizontal base table (not shown). The method for vertically calibrating is to install the vertical calibration device 1 to a base table so that and to make the surface PX1 and the surface PX2 parallel to the X axis, while making the surface PY1 and surface PY2 parallel to the Y axis. A driving machine is used to drive a (copper) wire having a tension on the wire and exert tension to the wire. Contact points on the surface PY1 and PX2 are first derived in X and V directions at the same time. Then, the same movement is performed simultaneously in another directions so as to acquire the contact points at the upper and lower positions of the surface PY1 and PY2. Thereby, the position of the vertical line is obtained.

[0003] The method for measuring the heights of the upper holding guide and lower holding guide of a wire cutting electric discharge machine through the automatically vertically calibrated apparatus 1 of the conventional cutting electric discharge machine is illustrated in FIG. 2. In FIG. 2, reference number 4 is a (copper) wire, 5 is an upper holding guide, and 6 is a lower holding guide. As illustrated in the drawing, the wire 4 is disposed at a position corresponding to a vertical line derived from the above-mentioned method. To obtain a distance x from the base table to the upper holding guide 5 and a distance y from the base table to the lower holding guide 6, at first, the upper holding guide 5 is displaced away from the position of the vertical calibration device along the X and U directions with a distance e as the tilt line 4′ shown in FIG. 2. Then, the upper holding guide 5 and lower holding guide 6 translate with a constant speed to the vertical calibration device 1 holding this tilt line 4′ until the wire 4 contacts with the lower calibration board 3 of the vertical calibration device 1. Accordingly, the tilt wire 4′ moves to the position of a tilt wire 4″ with a distance d. through a distance of d. After the upper holding guide 5, and lower holding guide 6, and wire 4 returns to the vertical position, the same method is used to move the lower holding guide 6 away from the vertical calibration device 1 at a distance e. Then, the tilt wire moves to find the contact point with the upper holding guide 2 of the vertical calibration device 1, as the tilt wire 4″′ shown in FIG. 2 so as to acquire the distance c. From the triangular relation of FIG. 2, we may derive:

X=[a(c-e)+b(e-d)]/(c-d)  (1)

Y=(bd-ac)/(c-d),  (2)

[0004] Where a, b, and c are known factors, and c and d are respectively the distances which the tilt wire has shifted after contacting the upper calibration board and lower calibration board. Thereby, x and y are the distances from the upper holding guide 5 to the table and from the lower holding guide 6 to the table, respectively.

[0005] However, this apparatus of prior art and the method for vertically calibrating a wire of a wire cutting electric discharge machine have the following disadvantages:

[0006] (1) the vertical calibration device 1 is required to be parallel to the base table, or otherwise calibrations in the X and Y directions for converging to a vertical position must be performed. However, to be parallel with the table for the calibration device is difficult, and inaccuracy of the vertical position will affect the precision of the upper holding guide and lower holding guide.

[0007] (2) When estimating the positions of the upper holding guide 5 and lower holding guide 6, equations (1) and (2) include two variables c and d which are difficult to measure and may enlarge the errors in calculating x and y to overcome the problem mentioned above, a method and apparatus of a ring-typed vertical calibration have developed.

SUMMARY OF THE INVENTION

[0008] Accordingly, the primary object of the present invention is to provide an apparatus and method for vertically calibrating a wire of a wire cutting electric discharge machine, wherein coaxial circles of the upper and lower sides and with different diameters are used to solve the parallelism problem of the apparatus with the base table, and increase the measuring speed and accuracy.

[0009] Another object of the present invention is to provide an apparatus and method for vertically calibrating a wire of a wire cutting electric discharge machine, wherein coaxial circles with different diameters at the upper and lower sides are used, the cone angle is used for the calculation of the heights of upper holding guide and lower holding guide to increase measurement accuracy.

[0010] A further object of the present invention is to provide an apparatus for vertically calibrating a wire of a wire cutting electric discharge machine, wherein the apparatus will diminish the possibility of a copper wire in contact with the calibrator so not to affect the accuracy in calibration.

[0011] To achieve above objects, the present invention provides an apparatus for vertically calibrating a wire of a wire cutting electric discharge machine, which includes: a main body having a flat bottom, an upper calibration board and a lower calibration board insulated from and connected to one lateral surface of the main body; an upper calibration board with a circle and an lower calibration board with a circle, wherein the upper circle and lower circles have different diameters but are coaxial. The vertical calibration device of the present invention is accommodated to a machine controller to detect whether a circle is in contact with a wire. First, set the calibration device on the base table. Since the upper circle and lower circle are coaxial circles, it is unnecessary to consider the direction of the apparatus. A wire having a tension on it passes through the circles, then, the wire is moved to contact the upper circle and lower circles to determine the centers of the upper circle and lower circles and therefore the calibration is accomplished. Whereby the present invention improves measuring accuracy and speed.

[0012] After calibration, since the height of the lower circle, the height of upper circle, the radius of upper circle, the radius of lower circle, and the cone angle of the two circles are all known in advance, the equation for acquiring the height of the upper holding guide contains only one variable, which is the translated distance of the wire in tension from the vertical position to the circle edge. The equation of the height of the lower holding guide also contains one variable estimated as the upper one. The prior art formula for deriving the height of the upper holding guide has two variables. The formula of the present invention has only one variable required to obtain the height of the lower holding guide. In the prior art formula, two values are necessary for acquiring the height of the lower holding guide value. Therefore, in the present invention, the heights of the upper holding guide and lower holding guide have less errors than the prior art in which two simultaneous linking equations are necessary to be solved. Therefore, the precision of the present invention is more accurate than the prior art.

[0013] In another embodiment of the present invention, the upper calibration board is divided into two parallel ones. One board is coplanar with lower calibration board, and the other is not. Therefore, utilizing this modification the heights of the upper and lower holding guide may be obtained by the method of the present invention.

[0014] The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In the accompanying drawings,

[0016]FIG. 1 is a schematic view of a prior art of a vertical calibration device 1 a.

[0017]FIG. 2 is used to describe the calculation of the heights of the upper holding guide and lower holding guide in the vertical calibration device of FIG. 1 of the prior art.

[0018]FIG. 3 is a schematic view of an embodiment of the vertical calibration device in the present invention.

[0019]FIG. 4 is the embodiment of the vertical calibration device of the present invention, wherein before calibration, the tilt wire passes through the upper circle and lower circle which are coaxial but have different diameters.

[0020]FIG. 5(A) shows the embodiment of the vertical calibration device in the present invention, wherein in the calibration process, contact points are found in the Y and V directions, where (b) is a perspective view and (a) is an upper view.

[0021]FIG. 5(B) shows the embodiment of the vertical calibration device in the present invention, wherein in the calibration process, contact points are found in X and U directions, where (b) is a perspective view and (a) is an upper view.

[0022]FIG. 6 is the embodiment of the vertical calibration device for the calculation of the heights of the upper holding guide and lower holding guide.

[0023]FIG. 7 is a schematic view of another embodiment of the vertical calibration device in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] In order that those skilled in the art can further understand the present invention, a description is given the following in detail. However, these descriptions and the appended drawings are only used to enable those skilled in the art to understand the objects, features, and characteristics of the present invention, but not to be used to confine the scope and spirit of the present invention defined in the appended claims.

[0025] Referring to FIG. 3, the schematic view of the apparatus for vertically calibrating a wire of a wire cutting electric discharge machine according to the present invention is illustrated. The vertical calibration device 1 a includes a main body 7 a, upper calibration board 2 a and a lower calibration board 3 a, which are insulated from and fixed to the main body 7 a. The upper calibration board 2 a, the lower calibration board 3 a, and the flat bottom of the main body 7 a are parallel to a base table of the discharging machine. The upper calibration board 2 a has a upper circle C1, and the lower calibration board 3 a has a lower circle C2. The upper circle C1 and lower circle C2 are coaxial circles but different diameters. In this embodiment, the radius of the upper circle C1 is R, and the radius of the lower circle C2 is r, while R>r. The vertical calibration device 1 a to the controller (not shown) of a discharging machine may accommodate to detect whether a line is in contact with the upper circle C1 or lower circle C2.

[0026] When the vertical calibration device 1 a is used to calibrate the verticality of a line, it can then calculate the positioning of the upper holding guide and lower holding guide. At first, the vertical calibration device 1 a is fixed to the table (not shown). The upper calibration board 2 a and lower calibration board 3 a are parallel to the base table, while the upper circle C1 and lower circle C2 are within the traveling range of the machine. The height of the Z axis of the machine is adjusted to be above the vertical calibration device 1 a so that as machine moves, it will not collide with the vertical calibration device 1 a. Moving the machine to the upper circle C1 and lower circle C2, a wire passes through the two circles as illustrated in FIG. 4. The upper holding guide 5 is above the upper circle C1 and lower holding guide 6 is below the lower circle C2. A wire 4 passes through the upper circle C1 and lower circle C2. When the wire 4 is not in contact with the upper circle C1 or lower circle C2, the wire is held in tension.

[0027] A process of automatic vertical calibration is initiated at first, as shown in FIG. 5(A), wherein (b) is a perspective view and (a) is an upper view. The machine moves along the directions of Y axis and V axis to look for the points P1 and Q1 which are the contacts points of wire 4 with the upper circle C1 and lower circle C2 respectively, recording the points. Then, moving along reverse directions of Y axis and V axis, the points P2 and Q2 being another contacts points of wire 4 with the upper circle C1 and lower circle C2 are searched, then the points are recorded. Then, move to middle point. Then, as shown in FIG. 5(B), where (b) is a perspective view, and (a) is an upper view, the machine moves along X axis and U axis to look for the points P3 and Q3 which are the contact points of wire 4 with the upper circle C1 and lower circle C2, and the points are then recorded. Then, moving along reverse directions of X axis and U axis, the points P4 and Q4 being another contact points of wire 4 with the upper circle C1 and lower circle C2 are searched, then the points are recorded. Then, move to the middle point. The middle point is the axis of the coaxial circles C1 and C2, i.e., the vertical position of the wire.

[0028] Of course, the axis of the coaxial circles C1 and C2 may be obtained from driving a center of a circle through three points. To improve the precision in the vertical calibration, using four points to acquire a center of a circle may be used, or many centers of circles may be obtained and then these centers are averaged.

[0029] To shorten the contact time of wire 4 with the vertical calibration device 1 a to a minimum so as to reduce the possibility of scraping, the step of acquiring the contact with the upper circle C1 and lower circle C2 at the same time can be acquired by the following way:

[0030] (1) The wire 4 moves near the upper circle C1 and lower circle C2 along a positive direction of the X axis and U axis with a predetermined speed until any contact on the circle is detected. Then, it is determined whether the wire is in contact with the upper circle C1 or lower circle C2 and the result is recorded.

[0031] (2) If the lower circle C2 is contacted, then wire 4 moves away from the lower circle C2 in the negative X direction with a predetermined speed. If the upper circle C1 is contacted, then wire 4 moves away from the upper circle C1 in the negative U axis with a predetermined speed until it no longer contacts with the circle.

[0032] (3) If the previous contact position is the lower circle C2, then wire 4 moves near the two circles along a positive direction of the U axis with a predetermined speed until it is in contact with one of the two circles; if the previous contact position is upper circle C1, then wire 4 moves near the two circles along a positive direction of the X axis with a predetermined speed until it is in contact with one of the two circles. It is determined whether the contacted circle is the upper circle C1 or the lower circle C2, and then the result is recorded.

[0033] (4) If the contact position is the lower circle C2, the wire moves from the lower circle C2 along the negative direction of the X axis with a predetermined speed. If the contact position is the upper circle C1, the wire moves from the upper circle C1 along the negative direction of U axis with a predetermined speed until then it is no longer in contact with the circle.

[0034] (5) Determine the contact position in step (3), if the contact position is the same as the former one, upper circle C1 or lower circle C2, then the process returns to step (3). If the contact position is not the same as the previous one, i.e., if the contact position of the upper circle C1 and lower circle C2 are alternated, then the operation of finding the position of a circle is complete.

[0035] (6) The step (1) to step (5) are repeated several times (according to the precision required). Each time, the moving speed is reduced. Therefore, the positions where wire 4 contacts the upper circle C1 and lower circle C2 at the same time are found.

[0036] The same method can be used to detect the negative direction of the X axis, the positive direction of the Y axis, and the negative direction of the Y axis. The positions where wire 4 contacts the upper circle C1 and lower circle C2 at the same time are all found. With these steps, the time period that takes for the copper wire 4 to contact the upper circle C1 and lower circle C2 are shortened. Further, no pressure is applied between the wire and circle, thereby reducing the possibility of scraping.

[0037] After completing the line vertical calibration, then the positions of the upper holding guide and lower holding guide are calculated. With reference to FIG. 6, after calibration, the data in the drawing can be obtained, wherein a is the height of the lower circle C2, b is the height of the upper circle C1, R is the radius of the upper circle C1, r is the radius of lower circle C2, and θ is half of the cone angle of the two coaxial circles. These are intrinsic data measured in advance of the vertical calibration device 1 a of the present invention. The values of c and d can be obtained by controller who detects the movement of the wire cutting electric discharge machine. Namely, these are acquired from the movement from the vertical position to any original position in finding an edge. Therefore, the heights of the upper holding guide 5 and lower holding guide 6, x, y are:

x=b+(d-R)/tan (θ)  (3)

y=(r-c)/tan (θ)-a  (4)

[0038] In above formulas, the equation for acquiring x only contains a variable d. The formula of the prior art (1) for deriving x value has two variables c, d. The above formula (4) has one variable for acquiring y value. In the formula of the prior art (2), two values c, d are necessary for deriving the y value. Therefore, in the apparatus of the present invention, the heights of x and y of the upper holding guide 5 and lower holding guide 6 has less error than the prior art in which two simultaneous linking equations are necessary to be solved. Therefore, the precision of the present invention is better than the prior art.

[0039] In the above embodiment, the radius R of the upper circle C1 is larger than the radius r so of the lower circle C2, however, in other embodiments, the radius R of the upper circle C1 may be smaller than the radius r of the lower circle C2 or the two circles may have the same radii.

[0040] In the present invention, the heights of the upper holding guide 5 and lower holding guide 6 are measured by known tilt angle. However, it can be embodied by other embodiment. In the embodiment illustrated in FIG. 7, the main body 7 b of the automatic vertical calibration device 1 b has as an upper calibration board 2 b having a surface PX1 which is on the same plane of the surface PX2 of the lower calibration board 3 b. The surface PY1 of the upper calibration board 2 b is on the same plane of the surface PY2 of the lower calibration board 3 b. The surface PX1 and surface PX2 are vertical to the PY1 surface and PY2 surface, and these surfaces all are vertical to the table (not shown). The surface PX3 of the upper calibration board 2 b is not on the same plane of the surface PX2 of the lower calibration board 3 b, but is parallel to the surface PX2. The surface PY3 of the upper calibration board 2 b is not on the same plane with the surface PY2 of the lower calibration board 3 b, but is parallel to the surface PY2.

[0041] This automatic vertical calibration device 1 b is used in automatically vertically calibrating and measuring the upper holding guide 5 and lower holding guide 6 of a wire cutting electric discharge machine where at first, the surface PX1 and surface PX2 are parallel to the X axis of the table. The surface PY1 and surface PY2 are parallel to the Y axis. The machine is used to drive the (copper) wire to move so as to yield a tension in a wire. At first, the contact points of the surface PY1 and surface PX2 in the X and U directions are attained, or the contact points of the surface PY1 and surface PY2 in the Y and V directions are attained. Then the position of the vertical line is derived. This is identical to the prior art. But in measuring the heights of the upper holding guide 5 and lower holding guide 6, the method of the present invention can be used. Since when wire 4 is in contact with the surface PX3 of the upper calibration board 2 b and the surface PX2 of the lower calibration board 3 b, the angle between the tilt wire 4 and the vertical line is known, thereby the values of x and y can be obtained by formulas (3) and (4). Furthermore, the heights of the upper holding guide 5 and lower holding guide 6 can be measured by the surface PY3 of the upper calibration board 2 b and the surface PY2 of the lower calibration board 3 b.

[0042] In this embodiment, there may only be manufactured either more recessed or the surface PX3 and surface PX2. Moreover, these can be manufactured on the upper calibration board or lower calibration board.

[0043] The method and apparatus for vertically calibrating a wire of a wire cutting electric discharge machine of the present invention uses two coaxial circles at the upper and lower side having different radii. Two circles have respective detecting points for inputting data to the controller of the machine. By the circle detecting device, the centers of the two upper and lower two circles are obtained, namely, a vertical position is acquired. Therefore, the factors in other anisotropic directions can be cancelled. Unlike the conventional device, the error in calibration is reduced by the device having to be parallel or vertical to the conventional device. Therefore, the method of the present invention increases the precision and speed in measurement. In the present invention, by the known radii of two circles, the known heights of the two circles with respect to the table, the cone angle of known coaxial circles, and the displacement from a vertical position to any position of previous finding edge, the positions of the upper holding guide 5 and lower holding guide 6 can be acquired by one equation. Only one variable is in the equation which reduces the error. Therefore, the apparatus and method of the present invention may increase the measurement precision.

[0044] While the present invention is thus described as above, it will be obvious that it may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

We claim:
 1. A apparatus for vertically calibrating a wire of a wire cutting electric discharge machine comprising: a main body with a flat bottom and a plurality of lateral surfaces; an upper calibration board having an upper circle thereon and fixing to one lateral side of the main body to be parallel to a bottom of the main body; and a lower calibration board having an lower circle thereon and fixing to the lateral side of the main body to be parallel to a bottom of the main body; wherein the upper circle and lower circle are coaxial circles, the vertical calibration device is coordinated by a controller of the machine to detect whether a wire is in contact with the upper circle and the lower circle.
 2. The apparatus of claim 1, wherein the upper calibration board and lower calibration board are insulated and connected with the main body.
 3. The apparatus of claim 1, wherein the diameters of the upper circle and lower circle are different.
 4. A method for vertically calibrating a wire of a wire cutting electric discharge machine, comprising the step of: a. installing a circular type detecting device comprising an upper circle and a lower circle parallel to the table; wherein the two circle centers are coaxial for detecting whether a wire is in contact with the upper circle and lower circle; b. passing a wire through the upper circle and lower circle and then actuating the tension on a wire, so as to prevent the wire from being in contact with the circles; and c. moving the machine so that the wire is in contact with the upper circle and lower circle many times to acquire circle centers of the upper circle and lower circles, and passing the wire through the circle centers.
 5. The method of claim 4, wherein in step c of moving the machine to contact the wire with the upper circle and lower circle comprises the steps of: c1. the machine moves along the directions of Y axis and V axis (or X axis and U axis) to look for points which are the contact points of wire with the upper circle and lower circle, then recording the points; then, moving along reverse directions of Y axis and V axis (or X axis and U axis), wherein the points are other contact points of wire and the points are recorded with the upper circle and lower circle and are searched, then, movement to middle points is effected; and c2. the machine moves along X axis and U axis (or Y axis and V axis) to look for the points which are the contacts points of wire with the upper circle and lower circle, then recording the points; then, moving along reverse directions of X axis and U axis (or Y axis and V axis), the points being other contract points of wire with the upper circle and lower circle and are searched, then recording the points. then, movement to middle points is effected; wherein the middle point is shown to be the axial center of the coaxial circles, i.e., the vertical position of the wire.
 6. The method of claim 5, wherein the step of moving the machine so as to be in contact with the upper circle or the lower circle comprising the steps of: d1. Moving the wire approach to the upper circle and lower circle along a positive direction of the Y axis or V axis (X axis and U axis) with a predetermined speed until contact with any circle is detected; then, determining whether it is in contact with the upper circle C1 or lower circle, and then recording the result; d2. if the lower circle is contacted, then the wire removes from the lower circle in the negative Y direction (or X direction) with a predetermined speed; if the upper circle is contacted, then the wire removes from the upper circle in the negative V direction (or U direction) with a predetermined speed until it is not in contact with the circle; d3. if the previous contact position is the lower circle, then the wire moves near the two circles along the positive direction of the V axis (or U axis) with a predetermined speed until it is in contact with one of the upper circle or lower circle; if the previous contact position is upper circle, then the wire moves near the two circles along the positive direction of the Y axis (or X axis) with a predetermined speed until it is in contact with one of the upper circle or lower circle; determining whether the contact circle is the upper circle or the lower circle, and then recording the result; d4: if the contact position is the lower circle, removes from the lower circle along the negative direction of Y (or X) axis with a predetermined speed; if the contact position is the upper circle, removes from the upper circle along the negative direction of V axis with a predetermined speed until then it no longer contacts with the circle; d5; determine the contact position, if the contact position is the same as the former one, the upper circle or the lower circle, then the process returns to d3; If the contact position is not the same as the previous one, i.e., the upper circle and lower circle alternate, then the operation of finding the position of a circle can be completed; d6. step d1 to step d5 is repeated several times (according to the precision required); each time, the moving speed is recorded; therefore, positions where the wire contacts the upper circle and lower circle at the same time is found.
 7. The method of claim 5, wherein the heights of the upper holding guide 5 and lower holding guide x, y are: x=b+(d-R)/tan (θ)y=®-c)/tan (θ)-a where x is a height of the upper holding guide, y is a height of the lower holding guide, b is a height of the upper circle, a is a height of the lower circle, R is a radius of the upper circle C1, r is the radius of lower circle C2, and θ is one half of the cone angle of the two circles; the value of c is a movement of the lower holding guide from the vertical position to any original position in finding the edge in step c2; the value of d is a movement of the upper holding guide from the vertical position to any original position in finding the edge in step c2.
 8. An apparatus for vertically calibrating a wire of a wire cutting electric discharge machine, comprising: a main body with a flat bottom and a plurality of lateral surfaces; a first calibration board fixed to one lateral surface of the main body and being parallel to a bottom of the main body; the first calibration board having a first surface and a second surface perpendicular to the main body; and the first surface being vertical to the second surface; and a second calibration board fixed to one lateral surface of the main body, and being parallel to the bottom of the main body; the second calibration board having a third surface and a fourth surface perpendicular to the bottom of the main body; the third surface being coplanar with the first surface; the wire being in contact with the first surface and third surface; the fourth surface being coplanar with the second surface; the wire being in contact with the second surface and fourth surface; a fifth surface being at the second calibration board, which is parallel with, but not coplanar with the first surface, and the wire being in contact with the first surface and the fifth surface; wherein the vertical calibration device with a machine controller to detect that the wire is in contact with the surfaces of the first calibration board and second calibration board.
 9. The apparatus of claim 8, wherein the second calibration board has a sixth plane being parallel to the second surface but coplanar with the second surface and the wire are in contact with the second surface and the sixth surface.
 10. The apparatus of claim 8, wherein the first calibration board and second calibration board are insulated and connected to the main body. 